I'm using Opera from time to time, and the problem with EAB is that the line after the username isn't aligned to the line from a replying user.
Maybe an Opera bug (I've got version 6.01 right now and it works a treat), but maybe a HTML incompatibility as well.
It seems that the width of the table cell where the username and all the other stuff (time zone) is displayed varies, although it shouldn't do this.